Field of the Invention
The present invention generally relates to cleaning devices for mechanically cleaning optical fiber end faces and, in particular, to devices for cleaning lensed optical fiber end faces. Such optical fibers are typically installed in a ferrule connector, such as a plug or a bulkhead, for interconnection with another optical fiber or with an optoelectronic device.
In fiber optic networks, optical fiber strands, which typically are encased in a sheath disposed around the fiber optic core and have a core diameter of about 8 micrometers, are connected to each other by placing the ends of the optical fiber strands in abutting contact with each other. As is well known, one or more of the strands may be encased in protective jackets to form fiber optic cables. Two such cables may be connected to each other by placing the cable ends together in abutting contact with each other, with the optical fiber strands of one cable in alignment with those of the other cable. To do this, the ends of the individual fiber optic strands or cables are typically stripped of their protective jackets and bonded to and encased in the center of a rod-like ceramic ferrule, with the end of each optical fiber strand exposed in the end face of the ferrule.
All fiber optic connections are highly susceptible to contamination at the abutting end faces of the optical fiber ferrules. Specifically, the optical transmission capability of the junction between the optical fibers can be significantly impaired by microscopically small contaminant deposits on the end surfaces of the fibers. Sources of such contamination include smoke, dust, dirt, moisture and other ambient contaminates; oils, salts and particles transferred from the skin of technicians during connector manufacture and assembly, cable installation, or job site service work. Small amounts of contamination in the form of particles or haze will significantly increase light attenuation across the abutted connection. Therefore, it is essential that the optical fiber end faces be thoroughly cleaned before the optical fiber ends are connected in light-transmitting relationship to each other, and/or reconnected after they become contaminated during normal use and maintenance.
Some optical fiber ferrules have lensed ferrule end faces and are more commonly known as expanded beam (“EB”) ferrules. Among the advantages of EB ferrules as compared to non-EB ferrules are that the EB fiber optic ferrules show a greater tolerance for particulate contamination and provide some physical protection of the end of the optical fiber core. In addition, inasmuch as there is an air gap between mated lenses of EB fiber optic ferrules lower mating forces are required to make and hold the connection. Such EB ferrules have a lens at the end face of the ferrule which lens may be an imaging lens or, more commonly, a collimating lens. When two optical fibers having lensed ferrule end faces are to be connected, their respective convex surface lenses face each other with a small air gap between the lenses. Adequate cleaning of such EB fiber optic ferrule end faces present difficulties not encountered in cleaning the end surfaces of non-lensed, i.e., non-EB, fiber optic ferrule end faces.
Related Art
One practice in the cleaning of optical fiber connectors is to rub each ferrule end face against a fabric- or paper-based cleaning strip, sometimes using a cleaning solvent such as alcohol. This method requires that the ferrule end face be fully exposed for proper cleaning, but this is often impractical because the ferrule end face is often recessed within a connector or coupler and it would be necessary to disassemble the connector or coupler in order to clean the ferrule end face. In these circumstances, the ferrule end face is sometimes cleaned using a swab.
U.S. Pat. No. 7,401,374 “Article For Cleaning Optical Fibers” issued on Jul. 22, 2008 and related (divisional) U.S. Pat. No. 7,685,668, “Article For Cleaning Optical Fibers”, issued on Mar. 30, 2010, both to Jay S. Tourigny, and are assigned to the assignee of this application. Both these patents, the entire subject matter of which is incorporated by reference herein, concern cleaning devices for cleaning the ferrule end surfaces of optical fibers. The patented cleaning devices comprise a coherent body having a cleaning head in the form of a swab of thermally sintered polymer particles or polymer fiber strands, or a mixture of such particles and strands, having an open-cell structure. The patented devices comprise cleaning heads having zones of different polymer density and are well adapted to cleaning non-lensed, that is, non-EB, ferrule end faces of an optical fiber, particularly when the end face is recessed within a connector or coupler. Reducing polymer density in a given zone is attained by increasing the porosity of the polymer in such zone. Column 4, lines 55-61 of U.S. Pat. No. 7,685,668 discloses a compression zone pore volume of about 20% to about 80%, e.g., 50%, of the volume of the porosity matrix. The compression zone is that zone of the cleaning head which terminates in a contact area which contacts the ferrule end to be cleaned. The increased pore volume of the compression zone both enhances its cleaning ability (column 6, lines 21-36) and reduces the amount of force required to make the cleaning head conform to the shape of the ferrule end being cleaned (column 6, lines 37-39). Cleaning is carried out by rotating the cleaning device swab with the cleaning head pressed against the ferrule end face.
The aforesaid U.S. Pat. Nos. 7,401,374 and 7,685,668 describe an advance in the art in that the thermally sintered polymers eliminate a potential source of loose or broken fiber contamination and the zones of different polymer density facilitate thorough cleaning of the optic fiber ferrule ends as well as the side walls of the connector device connecting the ferrules to each other. However, the significantly different geometry of EB ferrule ends as compared to non-EB ferrule ends limits the effectiveness of prior art swabs for cleaning EB ferrule ends.
U.S. Pat. No. 5,925,191, issued on Jul. 20, 1999 to Stein et al., discloses a “rod” for cleaning and/or polishing various ferrules in a fiber optic connector. As illustrated in FIG. 1, the end face of optical fiber 103 and ferrule 104 are cleaned by contact with the end face at the bottom of the rectilinear hole 106. See column 4, lines 16-23. FIGS. 3 and 4 of Stein et al. are cross-sectional views of other embodiments of the cleaning rod having rectilinear openings at opposite ends. The embodiment of FIG. 4 includes a curved concave working surface 129 at the closed end of rectilinear hole 125. See column 5, line 43 et seq. As described at column 5, lines 53-57, the working surface 129 has a concave curve larger than the corresponding radius of the convex surface of the end face of a typical ferrule 104 (FIG. 1), so that the working surface 129 does not cut into the end face of the ferrule during polishing.
U.S. Pat. No. 6,810,552, issued on Nov. 2, 2004 to Miyake et al., discloses in FIG. 1 a cleaner 21 retained in a holding tool 22 which is described starting at column 4, line 19. As shown in FIG. 2, the cleaner 21 comprises a cylindrical main body 24 and a plug 25 fitted within the main body 24. Main body 24 is comprised of layers of polyester cloth adhered to each other with an adhesive and has a ferrule insertion hole 26 formed in the distal end of the body 24. See column 4, lines 26 et seq. The plug 25 is formed in a similar manner except in the shape of a solid cylinder rather than a tube. See column 4, line 51 et seq. Cleaning is accomplished as described starting at column 4, line 65, and illustrated by FIG. 2, which shows ferrule 12 aligned with hole 26 of the cleaner. The other embodiments illustrated in the remaining figures of Miyake et al. have in common the hollow tubular cylindrical member terminating in an inner wall (27 in FIGS. 1 and 2, 34 in FIGS. 3A-4B, etc.). The inner walls serve to contact and clean the end of the ferrule.